This application covers four basic areas of research: I. Investigate the structural changes accompanying the formation, dissolution and chemical repair of mineralized tissues. X-ray image magnifier microradiographic technique, with conventional X-ray sources and high energy synchrotron radiation will be used. This technique provides an improved,non-destructive and noncontaminating method of assessing the mineral content in various parts of the lesion. Benefits include a better understanding of prevention and restitution of carious lesions. II. Establish crystal-chemical relationships between octacalcium phosphate (OCP) and hydroxyapatite and related compounds. The objectives are to establish the kinetics, compositions, mechanism of formation and possible structure-dependent relationships between the various products involved in biomineralization. The benefits include a better understanding of the properties of nonstoichiometric bioapatites and the mechanisms of biomineralization processes. III. Establish crystal structures of compounds of interest to dentistry. The types of compounds include impure and substituted apatites, calcium pyrophosphates relevant to biominerals, hydrated phosphatic compounds which may act as nucleators during the formation of biominerals and double salts of calcium dicarboxylates with OCP. Single crystal X-ray and neutron diffraction techniques will be used. The benefits include a better understanding of the properties and mechanisms of formation of biominerals. IV. Studies are proposed to gain information which can help further improve the properties of a self-setting calcium phosphate cement (CPC) developed under this project. The setting reactions and compressive and diametral tensile strengths of CPC will be correlated with the crystallinity and particle size distribution of the cement ingredients.